The devices for regulating the speed of a wheel, also termed rotor, by a magnetic coupling, also termed magnetic link, have been known for many years. The clock application is also known. Numerous patent applications relating to this field have been filed by the company Horstmann Clifford Magnetics for the inventions of C. F. Clifford. In particular documents FR 1,113,932 and U.S. Pat. No. 2,946,183 will be cited. There is also known from the Japanese utility model JPS 5263453U (application No. JP19750149018U), a magnetic escapement of the same type with a direct magnetic coupling between a resonator and an escapement wheel formed by a disc supporting two coaxial annular magnetic tracks. These two tracks are substantially contiguous and each comprise magnetic zones formed by individual plates made of high-permeability magnetic material which are designed regularly with a given angular period, the plates of the first track being offset or phase-shifted by a half-period relative to the plates of the second track. Between the plates, non-magnetic zones are provided, i.e. zones with poor magnetic permeability. Thus high-permeability magnetic zones distributed alternately on both sides of a circle corresponding to the rest position (zero position) of at least one magnet carried by the end of a branch of a resonator of the tuning fork type are obtained. The magnet of the resonator is coupled magnetically to these two phase-shifted tracks such that it is attracted alternately by the magnetic zones of the first track and of the second track. The escapement wheel thus rotates with a speed of rotation such that it advances by one angular period of the two tracks at each oscillation of the resonator. The escapement wheel provides the energy necessary to maintain the oscillation of the branch of the resonator carrying the magnet of the magnetic coupling and this resonator controls or regulates the speed of rotation of this escapement wheel, which is proportional to the resonance frequency. There is thus a magnetic escapement connected to a resonator which together form a device for regulating the operation of a counting mechanism of a clock movement.
It will be noted that regulating devices of the previously mentioned magnetic type are provided in prior art for resonators which have a single degree of freedom for each part subject to a resonance movement. In general, the resonator is designed such that the magnet, carried by an element subject to a resonance movement, oscillates according to a substantially radial direction, i.e. substantially orthogonal to the two annular magnetic tracks. In this case, the mentioned embodiments of the prior art have the advantage of having a frequency reduction between the frequency of the oscillation of the resonator and the rotation frequency (in revolution/s) of the escapement wheel carrying the magnetic structure. No pivoted moving body rotates or oscillates at a frequency of the order of magnitude of the resonance frequency. The reduction factor is given by the number of angular periods of the annular magnetic tracks.
In the case of these resonators with a single degree of freedom, the above-mentioned advantage, following a frequency reduction between the oscillation of the resonator and the rotation of the escapement wheel, has a corollary which presents a problem for the magnetic coupling force. In fact, in order to increase the frequency reduction, it is necessary to increase the number of periods of the magnetic tracks. For a given diameter of the escapement wheel, an increase in the number of periods results in a decrease in the surface of the magnetic zones of the annular tracks. As the magnet of the resonator extends over an angular distance less than a half-period of the annular tracks, the dimensions of this magnet must also decrease when the frequency reduction increases. It is therefore understood that the magnetic interaction force between the resonator and the escapement wheel decreases; which limits the torque which can be applied to the escapement wheel and therefore increases the risk of loss of synchronisation between this resonator and this escapement wheel. There is understood here by synchronisation, a determined proportional relationship between the resonance frequency and the frequency of rotation of the escapement wheel.
Finally, it will be noted that clock regulating devices of the magnetic type comprising a resonator with two degrees of freedom, in particular a resonator, the inertial part of which has a trajectory in translation substantially describing a circle, by rotating continuously in the same direction, are not known. A requirement to design escapements of the magnetic type for such resonators with two degrees of freedom, with a decrease in the level of magnetic coupling, does however exist in the field of timepieces. This requirement even seems crucial when the resonator functions at a relatively high resonance frequency, for example resonators, the resonating element of which rotates at a frequency greater than ten revolutions per second (10 revolution/s=10 Hz). In fact, a mechanical coupling which would consist of connecting such a resonating element to a moving body would result in setting this moving body in rotation at the resonance frequency. A pivoted moving body with a rotation frequency greater than five or six revolutions per second poses a major problem of loss of energy by friction and a problem of wear and tear at the level of the bearings.